One guy I work for does a fair amount of business with the government (state and fed) and he always is able to get a card from them. Compare that with 45+ days to pay and it makes good sense. Especially if some bean counter sees the invoice and asks for extra documentation or other waste of time.
I choose to accept cards with no questions asked because it creates goodwill with the customer. The customer is always right. If they want to pay you with a card then that must be because it works for them financially so who am I to refuse that? I don't see any need to raise my rate over it because I feel it could more than pay for itself by way of making a sale where one otherwise would not have been made, or by getting full pay on site when otherwise I might have had to try and collect money.
As to the costs, Square, Intuit and Paypal basically charge all the same rates and are the lowest in the credit card industry, with no fixed costs and no investment required (other than a smart phone which I found useful for all kinds of things). There is an upstart that goes by the cute name "Rectangle" which is slightly lower and seems more aimed toward established businesses with less of the hipster influence as Square. They promise not to hold onto your money as Square reportedly sometimes does.
I am on Square and they have been good to me so far. I suppose Intuit would make the best sense if I was on Quickbooks but I am not.